Optical glass

ABSTRACT

AN OPTICAL GLASS IS DISCLOSED WHICH CONSISTS ESSENTIALLY OF (A) A GLASS BASE CONSISTING OF B2O3, LA2O3 AND SIO2, (B) OF ZRO2 AND TA2O5, AND (C) OF AT LEAST ONE CONSTITUENT SELECTED FROMA GROUP INCLUDING THE OXIDES AND FLUORIDES RESPECTIVELY OF SUCH METALS AS MAGNESIUM, CALCIUM, BARIUM, ZINC, LEAD, ALUMINUM, YTTRIUM, TITANIUM, NIOBIUM, AND TUNGSTEN. THE INDEX OF REFRACTION OF THE INVENTED GLASS RANGES IN DEPENDENCE ON THE PERCENTAGE OF THE INDIVIDUAL COMPONENTS FROM 1.80 TO 1.92 WHILE THE ABBE NUMBERS ARE BETWEEN 48 AND 35.0.

Feb. 16, 1971 BROMER ETAL 3,563,773

OPTICAL GLASS med my 29, 1969 En: r L 17 7'2 //V VE N TORS v Max:4 3 6 m, 1/ J) United States Patent 3,563,773 OPTICAL GLASS Heinz Briimer, Hermannstein, and Norbert Meinert and Ernst Leitz, Wetzlar, Germany, assignors to Ernst Leitz, G.m.b.H., Wetzlar, Lahn, Germany Continuation-impart of application Ser. No. 563,867,

July 8, 1966, which is a continuation-in-part of application Ser. No. 786,726, Jan. 14, 1959. This application May 29, 1969, Ser. No. 829,033 Claims priority, application Germany, Feb. 19, 1958,

29,720, Patent 1,061,976

Int. Cl. C03c 3/08 US. Cl. 106-54 11 Claims ABSTRACT OF THE DISCLOSURE An optical glass is disclosed which consists essentially of (a) a glass base consisting of B 0 Lagos and S102, (b) of ZrO and Ta O and (c) of at least one constituent selected from a group including the oxides and fluorides respectively of such metals as magnesium, calcium, barium, zinc, lead, aluminum, yttrium, titanium, niobium, and tungsten. The index of refraction of the invented glass ranges in dependence on the percentage of the individual components from 1.80 to 1.92 while the Abb numbers are between 48 and 35.0.

Our present application is a continuation-in-part application of our copending application Ser. No. 563,867, filed July 8, 1966, in the United States Patent Ofiice, which itself is a continuation-in-part application of our further copending application Ser. No. 786,726, filed Jan. 14, 1959, in the United States Patent Oflice, both of which applications are abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION The invention relates to an optical glass having a high index of refraction (n,,) and a relatively high Abb number (v and also having a high chemical resistance and stability, hardness and other properties requisite for an optical glass.

Although optical glasses having relatively high indices of refraction whose main constituents are lanthanum oxide (La o and boric oxide (B 0 are known, achievement of high indices of refraction by increasing the proportion of lanthanum oxide has been unsuccessful due primarily to the tendency of high lanthanum oxide-content glasses to devitrify. Secondarily, such glasses decrease the Abb value markedly. Silica (SiO has been used in very small proportions to stabilize the lanthanum oxide effect of devitrification.

It is the object of this invention to provide an optical glass overcoming such limitations having nevertheless extremely high proportions of lanthanum oxide together with relatively high proportions of boric oxide (B 0 and silica (silicon dioxide) (SiO The glass of the present invention consists of 62.5 to 80% of a glass base of boric oxide (B 0 silica (SiO and lanthanum oxide (La O in proportions lying within the boundary of the area outlined in the ternary diagram shown in the accompanying drawing. The balance of the glass consists of 5 to 12.5% of zirconium dioxide, of 7 to 18.5% of tantalum pentoxide, and of at least one of certain additives which may alter the index of refraction and Abb number or may be useful in modifying other physical properties of the glass.

In addition, we have found that the sum of the glass former constituents of the glass base, namely silica and boric oxide should be in sum 12.5 to 21% of the total weight, and the modifying oxide portion of the glass "ice.

base, namely the lanthanum oxide, should be within the range of 50 to 64% of the total weight.

Glasses made in accordance with this invention have indices of refraction (12,) within the range of 1.80 to 1.92, having corresponding Abb values (v ranging between 48 and 35.0.

As shown in the accompanying drawing, the ternary diagram therein represents the range of the three components of the glass base. The points connecting the lines defining the area within which the glass bases of the invention are located are identified according to the following Table 1.

TABLE 1 Percent of weight of glass base Boric Lanthanum Silica oxide oxide (S10 (B 0 (Lagos) As well understood in this art, the ternary diagram plot of the ranges of glass base weights by percent of the glass base which in turn, according to the invention, is within the range 62.5 to of the total weight of the glass, is such that the determination of any two of the constituents inherently dictates the percentage of the remaining constituent. Thus, for example, if one were to use a glass base having 80% of lanthanum oxide and 10% of silica, the glass base must have 10% boric oxide. To the glass base so determined 5 to 12.5% of zirconium dioxide and 7 to 18.5 of tantalum pentoxide are added and, further, there is added at least one additional oxide or fluoride respectively, preferably in the ranges according to the following Table 2, which oxides and fluorides are in themselves well known in the glass art to have certain influencing effects on the optical and physical properties of the glass.

TABLE 2 Percentage of Constituents additional to the glass base total weight I*[eryllium oxicilg 03610) O-3 agnesium ox e g0)...

Magnesium fluoride (MgFz) 1 Calcium oxide (CaO) l 0-3 Calcium fluoride (Cel a). Barium oxide (BaO) 0-3 Zinc oxide (ZnO) r 0-6 Cadmium oxide (CdO) 0-6 Lead oxide (PbO) 0-10 Aluminum oxide (A1203) 0-12. 5 Yttrium oxide (YzOs) Titanium dioxide (TiOz) 0-7. 5 Niobium pentoxide (Nb 0 0-5 Tungsten trioxide (W0 0-3 Sodium aluminum fluoride (NEIQAIFU) 0-1. 0

According to the invention glasses of desirable optical properties are achieved by the addition of at least one of constituents listed in Table 2 within the ranges indicated. However, special attention is drawn to the fact that of magnesium oxide and magnesium fluoride together only 03% of the total weight are to be added to the glass base. In like manner only a total of 03% of calcium oxide and of calcium fluoride together is to be present in the glass, and, further, the percentage of these constituents together with barium oxide is to remain well in the range of 03% as indicated in Table 2 by the brackets.

It will also be appreciated that for the convenience of the tabulation of the additional constituents we have indicated the value zero for those constituents which are not needed or desired for the glass chosen. Thus, as will be appreciated from the specific examples to be tabulated, infra, aluminum, yttrium, titanium, zirconium, are useful for improving hardness of the glasses. The heavy metal 3 4 oxides, such as tungsten trioxide, tantalum pentoxide, niotions of the glass base, namely the arithmetic sum of the bium pentoxide, lead oxide, titanium dioxide, are useful percent by total weight of the oxides of silicon and boron for increasing the index of refraction. Thus in certain for each example. glass the combination of such metal oxides with the lan- For illustration purposes, referring to Example 900/2, thanum oxide of the base contribute in combination to the we prepared a batch formulation of the constituents listed higher indices of refraction achieved by this invention. in Table 3 of a total weight of 5 kg. Initially, the constit- Further, as it will be appreciated to those skilled in this uents are intimately mixed and thereafter melted in a art, the ditficulty of using one or more of the well known platinum crucible at a temperature of 1300 to 1350 C. constituents for achieving certain desirable characteristics After fusion has been completed the temperature is raised of a glass is inhibited or proscribed by the deleterious efto 1400 C. and the melt is refined while continuously fect of the combinations with other constituents resulting stirring. The refining time for this step usually is 120 in devitrification and other undesirable effects, such as min te At th d of th refining period the furnace is chemical instability and poor machining properties. shut off and the melt is cooled to a temperature of 1280 For Certain glass We have found that the use Of the C. with continuous agitation. After that temperature has valent elements, as afiuoride, allows the glass to be melted been reached cooling is coninued without agitation to a substantially more easily. Such fluorides are calcium fiuortemperature b t 12()() C, At thi temperature the melt barium fluoride, efy01itea1S0 known as Sodium is poured into preheated molds and is cooled thereafter in aluminum fluoride. Yttrium oxide is also useful as an althe manner ll known i i e tenta i t aluminum oxide and is especially advantage In addition to the very high index of refraction of 1.900 ous when extreme value of the index of refraction and of and an e value f 404 this example has the charaethe dispersion Value (Abbe number) are heededteristic of a coefiicient of expansion (commonly desig- We have found more Particularly, according to the nated by a) of 7.3 10 The transformation point of Ventioh, that the addition of ahlmihhm yttrium Oxide this example of optical glass is 692 C., its softening point, should be limited to a maxium of 12.5% by weight of the c and a density f 5 53 For tempering the glass entire IhiXthTea temperature of 730 C. is preferred.

It may be noted that the lanthanum oxide in the glass DESCRIPTION F TH PREFERRED base may range from 74% to 80%, and that as the EM D lanthanum oxide increases the combined amounts of SiO;

and B 0 decreases. Also within the limits set by any per- In the following Table 3, we tabulate fifteen examples, centage of lanthanum oxide, the SiO will range between of glasses made according to the invention, arranged gen- 10% and 21%, and that for any percentage of SiO; within erally to increase in the value of indices of refraction any of these ranges decreases, a percentage of B 0 within We) of each Starting With Example PKT31 having an this range increases. The percentage of any one of the deli 1-350 and ending with Example PKT98 Of The three constituents is, therefore, determined by the pertabulation is arranged such that the base constituents of 35 eentage of th other two, A the mo nt of the gla base oxides of silicon, boron and lanthanum are first listed at i th tot l glass m lt va ie within the range of 62.5% the top of the tabulation with values representing the pert 80%, the amounts of La O SiO and B 0 for any cent of each of the constituents relative to the glass base composition f h glass bas decreases proportionately. and Corresponding accordingly to Such Points as would be It is to be noted that optical glasses with extremely determined y the ternary agram. high values of refractive indices are achieved according Immediately below Such listing We tabulate the eohstitto this invention with a relatively small portion of silica vents first y the glass base Portions and below that the and boric oxide. Note the values of this portion of the additional constituents, each of which being represented glass as shown i T bl 3 along row 263, A can b y the Percent of the total Weight of h glass- Fohewihg appreciated from a study of Table 3, as the sum of these the listing of the constituents we have included the lndex id i d d, h greater must h h ddi i l of refraction e) for each example as Well as the Abbe stituents taken from the group of aluminum, yttrium, number t)- To better appreciate the relative proportions tantalum and niobium oxides (listed within Tabl 2 0f the glass base relative to the total Weight, We have P While the invention has been described in detail with vided such a value for each example as indicated by the reference to certain specific embodiments, various changes row designated EGG. In addition the row identified as and modifications will become apparent to those skilled 2GB represents the artimetic sum of the glass former porin the art.

TABLE 3 40. (l 40. 5 40. 4 30. .l 35. S

1 (ill. 45 (58. O 72.

What is claimed is:

1. An optical glass having an index of refraction (71,.) within the range of about 1.850 and 1.920 and a corresponding Abb value (y between about 43.2 and 35.8 consisting essentially of a glass base consisting of B La O and Si0 in relative amounts falling within the area ABCD of the ternary diagram of the accompanying drawing, of 5 to 12.5% of ZrO 7 to 18.5% of Ta O and at least one constituent of the group listed in Table 2 of the specification in amounts indicated in said table, the amount of said glass base being within the range of 62.5 to 80 percent of the total weight of the glass, the ratio of La O versus SiO plus B 0 being within the range of 2.8 to 4 of the total weight of the glass with the amount of La O ranging between 50-64%, the amount of Si0 ranging between 6.2516.8%, and the amount of B 0 ranging between 4-12.8% of said total glass weight, wherein the sum of said glass formers Si0 plus B 0 totals 12.5 to 20.8%.

2. An optical glass having an indexof refraction (n of 1.850 and a corresponding Abb value (v of 43.2 consisting essentially of the following constituents each in percent of the total Weight of the glass:

510 7.9 B 0 7.9 1.8. 0 63.2 A1 0 7.9 Zr0 5.2 T3205 7.9

3. An optical glass having an index of refraction (n of 1.874 and a corresponding Abb value (v of 41.3 consisting essentially of the following constituents each in percent of the total weight of the glass:

4. An optical glass having an index of refraction (n of 1.876 and a corresponding Abb value (v of 41.8 consisting essentially of the following constituents each in percent of the total Weight of the glass:

S10 7.84 B 0 7.84 La O 62.53 A1 0 2.84 ZI'Og T3205 Na AlF 0.99

5. An optical glass having an index of refraction (n of 1.881 and a corresponding Abb value (v.,) of 41.2 consisting essentially of the following constituents each in percent of the total weight of the glass:

SiO 9.5 B 0 8.0 Lagog CaO 2.0 ZTOZ 5.3 Ta O 17.2

6. An optical glass having an index of refraction (n of 1.883 and a corresponding Abb value (v of 41.0 consisting essentially of the following constituents each in percent of the total Weight of the glass:

SiO 9.5 13 0 8.0 1.3.203

6 BaO 2.0 ZI'OZ 5.3 T3 0 17.2

7. An optical glass having an index of refraction (n of 1.894 and a corresponding Abb value (v of 40.2 consisting essentially of the following constituents each in percent of the total weight of the glass:

sio 8.80 B 0 6.45 La O 53.00 BeO 2.0 ZnO 0.85 CdO 2.90 ZI'OZ 7.5 Ta O 18.0 W0 0.5

8. An optical glass having an index of refraction (n of 1.896 and a corresponding Abb value (v of 39.2 consisting essentially of the following constituents each in percent of the total weight of the glass:

SiO 9.5 B 0 8.0 La O PbO 5.0 ZrO 5.3 T3205 9. An optical glass having an index of refraction (n of 1.898 and a corresponding Abb value (v of 39.7 consisting essentially of the following constituents each in percent of the total weight of the glass:

SiO 9.95 B 0 8.2 143203 ZnO 0.55 ZrO 8.5 T8205 Nb O 2.0

10. An optical glass having an index of refraction (n of 1.900 and a corresponding Abb value (v of 40.5 consisting essentially of the following constituents each in percent of the total Weight of the glass:

810 9.75 B 0 7.60 1.8 0 55.75 ZnO 0.55

ZI'OZ T3205 11. An optical glass having an index of refraction (n of 1.919 and a corresponding Abb value (v of 35.8 consisting essentially of the following constituents each in percent of the total weight of the glass:

HELEN M. MCCARTHY, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,56L773 Dated February 16, 197].

Inventor(s) Heinz Bromer, Norbert Meinert, Ernst Leitz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line 54 "Na AlF should read Na AlF Column 3, line 16, "fiuor" should read fluorand line 51 "artimetic" should read arithmetic Column 4, line 15 "coninued" should read continued In TABLE 3 row 10, "MgF" should read MgF In claim 1, line 3 "(Ye)" should read (V In claim ll, line 6,

' 'B 0 58. O: should read B 0 8.0

Signed and sealed this 15th day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

